Mram structure and method of fabricating the same

ABSTRACT

A magnetoresistive random access memory (MRAM) structure includes a magnetic tunnel junction (MTJ), and a top electrode which contacts an end of the MTJ. The top electrode includes a top electrode upper portion and a top electrode lower portion. The width of the top electrode upper portion is larger than the width of the top electrode lower portion. A bottom electrode contacts another end of the MTJ. The top electrode, the MTJ and the bottom electrode form an MRAM.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a method of fabricating amagnetoresistive random access memory (MRAM), and more particularly to amethod of fabricating a top electrode of the MRAM.

2. Description of the Prior Art

Many modern day electronic devices contain electronic memory configuredto store data. Electronic memory may be volatile memory or non-volatilememory. Volatile memory stores data only while it is powered, whilenon-volatile memory is able to store data even when power is removed.MRAM is one promising candidate for next generation non-volatile memorytechnology. An MRAM cell includes a magnetic tunnel junction (MTJ)having a variable resistance located between two electrodes disposedwithin back-end-of-the-line (BEOL) metallization layers.

An MTJ generally includes a layered structure comprising a referencelayer, a free layer and a tunnel oxide in between. The reference layerof magnetic material has a magnetic moment that always points in thesame direction. The magnetic moment of the free layer is free, but isdetermined by the physical dimensions of the element. The magneticmoment of the free layer points in either of two directions: parallel oranti-parallel to the magnetization direction of the reference layer.

As dimensions of the MRAMs are scaled down, more digits are needed to bestored in a smaller area. An improved MRAM structure is thereforerequired in the field.

SUMMARY OF THE INVENTION

It is an objective of the present invention to provide an MRAM structurewhich solves the problems of the related arts.

According to a first preferred embodiment of the present invention, anMRAM structure includes an MTJ and a top electrode contacting a firstend of the MTJ. The top electrode includes a top electrode upper portionand a top electrode lower portion, and a width of the top electrodeupper portion is larger than a width of the top electrode lower portion.A bottom electrode contacts a second end of the MTJ, wherein the topelectrode, the MTJ and the bottom electrode form an MRAM.

According to a second preferred embodiment of the present invention, amethod of fabricating an MRAM structure includes providing a firstdielectric layer. Next, a bottom electrode material layer is formed tocover the first dielectric layer. After that, an MTJ composite layer isformed to cover the bottom electrode material layer. Later, a first topelectrode material layer is formed to cover the MTJ composite layer.Subsequently, the first top electrode material layer, the MTJ compositelayer and the bottom electrode material layer are patterned to form atop electrode lower portion, an MTJ and a bottom electrode. After that,a second dielectric layer is formed to cover the first dielectric layer,and a top surface of the second dielectric layer is aligned with a topsurface of the top electrode lower portion. Next, a second top electrodematerial layer is formed to cover the second dielectric layer. Finally,the second top electrode material layer is patterned to form a topelectrode upper portion, wherein the top electrode upper portionconnects to the top electrode lower portion, the top electrode upperportion and the top electrode lower portion form a top electrode, awidth of the top electrode upper portion is larger than a width of thetop electrode lower portion, and the top electrode, the MTJ and thebottom electrode form an MRAM.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 to FIG. 9 depict a method of fabricating an MRAM structureaccording to a preferred embodiment of the present invention, wherein:

FIG. 1 shows a stage of providing a first dielectric layer and a bottomcontact plug therein;

FIG. 2 is a method following FIG. 1;

FIG. 3 is a method following FIG. 2;

FIG. 4 is a method following FIG. 3;

FIG. 5 is a method following FIG. 4;

FIG. 6 is a method following FIG. 5;

FIG. 7 is a method following FIG. 6;

FIG. 8 is a method following FIG. 7; and

FIG. 9 is a method following FIG. 8.

DETAILED DESCRIPTION

FIG. 1 to FIG. 9 depict a method of fabricating an MRAM structureaccording to a preferred embodiment of the present invention.

As shown in FIG. 1, a substrate such as a silicon substrate is provided.Metal interconnections are disposed within the substrate. A firstdielectric layer 10 is formed to cover the substrate. At least onebottom electron contact plug 12 is embedded within the first dielectriclayer 10. The bottom electron contact plug 12 may include a metal layer14 and a barrier 16. The barrier 16 is optional. The metal layer 14 ispreferably tungsten. The barrier 16 can be tungsten nitride. A topsurface of the bottom electron contact plug 12 is aligned with a topsurface of the first electric layer 10. Next, a bottom electron materiallayer 18 is formed to cover and contact the first dielectric layer 10.After that, an MTJ composite layer 20 is formed to cover and contact thebottom electron material layer 18. Subsequently, a first top electrodematerial layer 22 is formed to cover the MTJ composite layer 20. The MTJcomposite layer 20 includes multiple material layers. For example, theMTJ composite layer 20 includes numerous ferromagnetic material layersand at least one insulating layer disposed between each of theferromagnetic material layers. The first dielectric layer 10 includessilicon oxide or silicon carbide nitride. The bottom electron materiallayer 18, the MTJ composite layer 20 and first top electrode materiallayer 22 may be respectively formed by a deposition process such as achemical vapor deposition, a physical vapor deposition or an atomiclayer deposition.

As shown in FIG. 2, the first top electrode material layer 22, the MTJcomposite layer 20 and the bottom electron material layer 18 arepatterned to form a top electrode lower portion 28, an MTJ 26 and abottom electrode 24. Refer to FIG. 1 and FIG. 2 together. A mask layer(not shown) is formed to cover the first top electrode material layer22. A position of the top electrode lower portion 28 is defined on themask layer by a photo mask 30. After that, the first top electrodematerial layer 22 is etched to form the top electrode lower portion 28.Subsequently, the mask layer is removed. Next, the MTJ composite layer20 and the bottom electron material layer 18 are etched by taking thetop electrode lower portion 28 as a mask to form the MTJ 26 and thebottom electrode 24.

As shown in FIG. 3, a spacer 32 is formed around the top electrode lowerportion 28, the MTJ 26 and the bottom electrode 24. Next, a seconddielectric layer 34 is formed to cover the first dielectric layer 10.The spacer 32 may be silicon nitride or other insulating materials. Thesecond dielectric layer 34 is a low-k dielectric material. For example,the second dielectric layer 34 may be a material which has a dielectricconstant lower than 2.7 such as silicon oxide carbides (SiOC). As shownin FIG. 4, the second dielectric layer 34 is planarized to make a topsurface of the second dielectric layer 34 align with a top surface ofthe top electrode lower portion 28. As shown in FIG. 5, a second topelectrode material layer 36 is formed to cover the second dielectriclayer 34. The second top electrode material layer 36 contacts the topelectrode lower portion 28. The first top electrode material layer 22and the second top electrode material layer 36 may independently includetantalum, titanium, tantalum nitride or other metal materials. Thesecond top electrode material layer 36 can be formed by a depositionprocess such as a chemical vapor deposition, a physical vapor depositionor an atomic layer deposition.

As shown in FIG. 6, the second top electrode material layer 36 ispatterned to form a top electrode upper portion 38. A width W2 of thetop electrode upper portion 38 is larger than a width W1 of the topelectrode lower portion 28. In detail, a mask layer (not shown) isformed to cover the second top electrode material layer 36. The positionof the top electrode upper portion is defined on the mask layer by thephoto mask 30. By adjusting the exposure references, the same photo mask30 used in FIG. 2 can be used to define a width larger than the width W1of the top electrode lower portion 28. Later, the second top electrodematerial layer 36 is patterned to form the top electrode upper portion38 by taking the mask layer as a mask. The top electrode upper portion38 connects to the top electrode lower portion 28. The top electrodeupper portion 38 and the top electrode lower portion 28 form a topelectrode 40. The top electrode 40, the MTJ 26 and the bottom electrode24 form a MRAM 100. At this point, the MRAM 100 of the present inventionis completed. Because the second top electrode material layer 36 isformed after forming the spacer 32, the spacer 32 does not surround thesidewall of the top electrode upper portion 38, but only contacts thebottom of the top electrode upper portion 38.

As shown in FIG. 7, a third dielectric layer 42 is formed to conformallycover the second dielectric layer 34 and the top electrode upper portion38. The third dielectric layer 42 is a low-k dielectric material. Forexample, the third dielectric layer 42 may be a material which has adielectric constant lower than 2.7 such as silicon oxide carbides(SiOC). Later, a dual damascene opening 44 is formed within the thirddielectric layer 42, the second dielectric layer 34 and the firstdielectric layer 10 at one side of the MRAM 100. The dual damasceneopening 44 includes a contact hole 44 a and a trench 44 b on the contacthole 44 a. The steps of forming the dual damascene opening 44 includeetching the third dielectric layer 42 and the second dielectric layer 34by taking the first dielectric layer 10 as an etching stop layer to forma hole in the third dielectric layer 42 and the second dielectric layer34. The hole has the same size as the contact hole 44 a. Later, afterdefining the position of the trench 44 b, the third dielectric layer 42and the second dielectric layer 34 around the hole are etched and thefirst dielectric layer 10 below the hole is also etched to form thetrench 44 b in the third dielectric layer 42 and in the seconddielectric layer 34 and to form the contact hole 44 a in the firstdielectric layer 10. As shown in FIG. 8, a barrier 46 and a metal layer48 are formed to fill in the dual damascene opening 44. The barrier 46and the metal layer 48 serve as a first dual damascene structure 50. Thefirst dual damascene structure 50 is a part of the metalinterconnection. According to another preferred embodiment, the barrier46 can be omitted. Next, a planarization process such as a chemicalmechanical planarization is performed to make the top surface of thethird dielectric layer 42, the top surface of the barrier 46 and the topsurface the metal layer 48 to align with the top surface of the topelectrode upper portion 38, i.e. the top surface of the first dualdamascene structure 50 is aligned with the top surface of the topelectrode upper portion 38. Furthermore, the bottom of the first dualdamascene structure 50 is aligned with the bottom of the bottomelectrode contact plug 12.

As shown in FIG. 9, a fourth dielectric layer 52 is formed to cover thethird dielectric layer 42. Next, two dual damascene openings 54/56 areformed within the third dielectric layer 42 to expose the top electrodeupper portion 38 and the first dual damascene structure 50,respectively. Then, a barrier 58 and a metal layer 60 are formed in thedual damascene openings 54/56 to complete a second dual damascenestructure 62 and a third dual damascene structure 64. The second dualdamascene structure 62 and the third dual damascene structure 64 serveas part of the metal interconnection. The second dual damascenestructure 62 contacts the top electrode upper portion 38. The third dualdamascene structure 64 contacts the first dual damascene structure 50.The second dual damascene structure 62 has a bottom surface contactingthe top electrode upper portion 38. The width W3 of the bottom surfaceis smaller than the width W2 of the top electrode upper portion 38. Themetal layers 48/60 of the first dual damascene structure 50, the seconddual damascene structure 62 and the third dual damascene structure 64can be copper, tungsten or other conductive materials. The barriers46/58 can be tungsten nitride or tantalum nitride.

It is noteworthy that, because the width W2 of the top electrode upperportion 38 is larger than the width W3 of the bottom surface of thesecond dual damascene structure 62, even though there is an etchingoffset during the formation of the second dual damascene structure 62,the dual damascene opening 54 can still stop within the range of thewidth W2 of the top electrode upper portion 38. Because the dualdamascene opening 54 is guaranteed to be stopped on the top electrodeupper portion 38, the second dual damascene structure 62 will notpenetrate too much of the second dielectric layer 34 and will not reacharound the MRAM 100 because of the etching offset. In the conventionalmethod, the dual damascene structure is prevented from being around theMRAM by increasing the total thickness of the top electrode to therebyincrease the distance between the dual damascene structure and the MRAM.The present invention does not need to increase the thickness of the topelectrode.

Because the thickness of the top electrode 40 is smaller than theconventional top electrode, the inner stress of the top electrode 40 ofthe present invention can be smaller. In this way, the MTJ 26 in theMRAM 100 receives less stress and the composite materials in the MTJ 26will not be torn off due to stress. Furthermore, the top electrode 40 ofthe present invention is formed in two steps including the steps ofmaking the top electrode upper portion 38 and the top electrode lowerportion 28, and the total thickness of the top electrode 40 of thepresent invention is smaller than in the conventional method. Therefore,under the circumstance of forming numerous MRAMs 100, during the step offorming the second dielectric layer 34, the recess 66 between the topelectrode lower portion 28, the MTJ 26 and the bottom electrode 24within two adjacent MRAMs 100 will not have a large aspect ratio and agap can be prevented from being formed in the recess 66.

As shown in FIG. 9, according to a second preferred embodiment of thepresent invention, an MRAM structure 200 includes an MTJ 26. A topelectrode 40 contacts an end of the MTJ 26. A bottom electrode 24contacts another end of the MTJ 26. The top electrode 40 includes a topelectrode upper portion 38 and a top electrode lower portion 28. The topelectrode upper portion 38 connects to the top electrode lower portion28. A width W2 of the top electrode upper portion 38 is larger than awidth W1 of the top electrode lower portion 28. The width W1 of the topelectrode lower portion 28 is the same as a width of the MTJ 26.Moreover, the top electrode lower portion 28 contacts the MTJ 26. Thetop electrode 40, the MTJ 26 and the bottom electrode 24 form an MRAM100. A bottom electrode contact plug 12 is disposed under the bottomelectrode 24 and contacts the bottom electrode 24. A first dualdamascene structure 50 is disposed at one side of the MRAM 100. The topsurface of the first dual damascene structure 50 is aligned with the topsurface of the top electrode upper portion 38. The bottom of the firstdual damascene structure 50 is aligned with the bottom of the bottomelectrode contact plug 12. The first dual damascene structure 50includes a metal layer 48 and a barrier 46. The barrier 46 is optional.

A second dual damascene structure 62 is disposed on the top electrode 40and contacts the top electrode upper portion 38. The second dualdamascene structure 62 has a bottom surface contacting the top electrodeupper portion 38. A width W3 of the bottom surface is smaller than thewidth W2 of the top electrode upper portion 38. A spacer 32 surroundsthe bottom electrode 24, the MTJ 26 and the top electrode lower portion28. The spacer 32, however, does not surround the top electrode upperportion 38. The spacer 32 only contacts the bottom of the top electrodeupper portion 38. The second dual damascene structure 62 includes ametal layer 60 and a barrier 58. The barrier 58 is optional.

The top electrode lower portion 28 and the top electrode upper portion38 may independently include titanium nitride, tantalum nitride or otherconductive materials. Similarly, the bottom electrode 24 can includetitanium nitride, tantalum nitride or other conductive materials. TheMTJ 26 includes numerous ferromagnetic material layers and at least oneinsulating layer disposed between each of the ferromagnetic materiallayers. The spacer 32 may be silicon nitride or other insulatingmaterials.

The metal layers 48/60 of the first dual damascene structure 50, and thesecond dual damascene structure 62 can be copper, tungsten or otherconductive materials. The barriers 46/58 can be tungsten nitride ortantalum nitride.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

1: A magnetoresistive random access memory (MRAM) structure comprising:a magnetic tunnel junction (MTJ); a top electrode contacting a first endof the MTJ, wherein the top electrode comprises a top electrode upperportion and a top electrode lower portion, and a width of the topelectrode upper portion is larger than a width of the top electrodelower portion; and a bottom electrode contacting a second end of theMTJ, wherein the top electrode, the MTJ and the bottom electrode form anMRAM. 2: The MRAM structure of claim 1, wherein the top electrode lowerportion contacts the MTJ. 3: The MRAM structure of claim 1, wherein thetop electrode upper portion connects to the top electrode lower portion.4: The MRAM structure of claim 1, wherein the width of the top electrodelower portion is the same as a width of the MTJ. 5: The MRAM structureof claim 1, further comprising: a bottom electrode contact plug disposedunder the bottom electrode and contacting the bottom electrode; and afirst conductive line disposed at one side of the MRAM, wherein a topsurface of the first conductive line is aligned with a top surface ofthe top electrode upper portion, and a bottom of the first conductiveline is aligned with a bottom of the bottom electrode contact plug. 6:The MRAM structure of claim 1, further comprising: a second conductiveline disposed on the top electrode and contacting the top electrodeupper portion, wherein the second conductive line has a bottom surfacecontacting the top electrode upper portion, and a width of the bottomsurface is smaller than the width of the top electrode upper portion. 7:The MRAM structure of claim 1, wherein the top electrode upper portioncomprises titanium nitride or tantalum and the top electrode lowerportion comprises titanium nitride or tantalum. 8: A method offabricating a magnetoresistive random access memory (MRAM) structurecomprising: providing a first dielectric layer; forming a bottomelectrode material layer covering the first dielectric layer; forming amagnetic tunnel junction (MTJ) composite layer covering the bottomelectrode material layer; forming a first top electrode material layercovering the MTJ composite layer; patterning the first top electrodematerial layer, the MTJ composite layer and bottom electrode materiallayer to form a top electrode lower portion, an MTJ and a bottomelectrode; forming a second dielectric layer covering the firstdielectric layer, wherein a top surface of the second dielectric layeris aligned with a top surface of the top electrode lower portion;forming a second top electrode material layer covering the seconddielectric layer; and patterning the second top electrode material layerto form a top electrode upper portion, wherein the top electrode upperportion connects to the top electrode lower portion, the top electrodeupper portion and the top electrode lower portion form a top electrode,a width of the top electrode upper portion is larger than a width of thetop electrode lower portion, and the top electrode, the MTJ and thebottom electrode form an MRAM. 9: The method of fabricating an MRAMstructure of claim 8, further comprising: before forming the bottomelectrode material layer, forming a bottom electrode contact plugembedded in the first dielectric layer, wherein the bottom electrodecontact plug is under the bottom electrode and contacts the bottomelectrode; and after forming the MRAM, forming a first conductive lineat one side of the MRAM, wherein a top surface of the first conductiveline is aligned with a top surface of the top electrode upper portion,and a bottom of the first conductive line is aligned with a bottom ofthe bottom electrode contact plug. 10: The method of fabricating an MRAMstructure of claim 8, further comprising: forming a second conductiveline on the top electrode and contacting the top electrode upperportion, wherein the second conductive line has a bottom surfacecontacting the top electrode upper portion, and a width of the bottomsurface is smaller than the width of the top electrode upper portion.11: The method of fabricating an MRAM structure of claim 8, furthercomprising: forming the top electrode lower portion by using a photomask to define a position of the top electrode lower portion; andforming the top electrode upper portion by using the photo mask todefine a position of the top electrode upper portion, wherein exposurereferences are different when forming the top electrode lower portionand forming the top electrode upper portion so as to make the width ofthe top electrode upper portion and the width of the top electrode lowerportion different from each other. 12: The method of fabricating an MRAMstructure of claim 11, wherein the steps of patterning the first topelectrode material layer, the MTJ composite layer and the bottomelectrode material layer comprises: defining the position of the topelectrode lower portion by the photo mask; patterning the first topelectrode material layer to form the top electrode lower portion; andpatterning the MTJ composite layer and the bottom electrode materiallayer by taking the top electrode lower portion as a mask to form theMTJ and the bottom electrode.